Field of the Invention
The present invention relates to a vehicle energy management device for managing energy consumption of a vehicle, and more particularly, to a vehicle energy management device suitable for a vehicle having a plurality of different energy sources.
Description of the Background Art
A vehicle that utilizes a plurality of different energy sources such as fuel energy and electrical energy, i.e., a so-called hybrid vehicle, has various operation modes in order to reduce an energy consumption amount. Examples of operation modes of a hybrid vehicle include, for example, a mode in which only power output from the engine is used as the power source to travel, a mode in which only power output from the motor is used as the power source to travel, a mode in which power output from both the engine and the motor is used as the power source to travel, and a mode in which engine output power is used to generate electricity, which is then stored or is used to drive the motor.
Switching control among these operation modes has conventionally been performed based on a current vehicle status determined from information obtained by an in-vehicle sensor (sensor information). That is, operation modes are switched over so that the energy consumption will be minimized, using sequential control in which the output power required for vehicle travel is calculated based on sensor information, and an optimum operation mode for obtaining the output power is then selected.
For example, Japanese Patent No. 3537810 discloses a technique in which a fuel consumption amount required for traveling by the engine, a fuel consumption amount required for traveling by the motor, and a fuel consumption amount required for traveling with the assistance of the motor (i.e., traveling that uses both engine output power and motor output power as the power source) are calculated and compared to select the power source that is substantially low in fuel consumption amount.
Japanese Patent No. 3894105 discloses a technique in which, when additional torque is generated in addition to base torque in order to obtain a required driving force, a comparison is made between the energy efficiency of the engine and the energy efficiency of the motor-generator during generation of the additional torque, and based on the comparison result, a torque generation ratio of the additional torque between the engine and the motor-generator is determined. Thus, this technique provides torque assist control of high energy efficiency.
Japanese Patent No. 3386044 discloses a technique of engine control, in which when a vehicle uses an idling stop function (automatic engine shutdown during stopping), it is determined whether air conditioning capability is available or not, and the engine is not started if such capability is available, and the engine is started if such capability is no more available, and once the engine is started, the engine is not stopped even if air conditioning capability becomes available. This technique can prevent a decrease in fuel mileage, and prevent discomfort from being caused by repetitive start-stop cycles of the engine.
A hybrid vehicle has a drawback in that motor drive using electrical energy, and electrical power regeneration by a regenerative brake during deceleration (electricity generation using kinetic energy of the vehicle), may be limited by the charge status of the storage battery on the vehicle. For example, when the charge level of the storage battery is low, the vehicle needs to travel only by the engine without driving the motor even if a high driving force is required on a rising grade, and thus the fuel mileage is decreased. Conversely, when the charge level of the storage battery is near an upper limit, regenerated electrical power cannot be charged to the storage battery, and therefore the regenerative brake cannot be used even if regeneration can be performed on a downgrade. This necessitates use of a friction brake, which will waste kinetic energy as heat.
When traveling a route including both an urban road and a highway, it is considered that high energy efficiency is achieved by traveling with the motor in the urban area, and traveling with the engine on the highway. Thus, it is preferred that, near the exit of highway, the operation mode be changed to a mode in which the charge level of the storage battery is made high such as, for example, an operation mode in which electricity is generated using engine output power. However, with the conventional method in which the operation mode is selected based on current sensor information, the timing to start electricity generation using engine output power cannot be determined. Thus, the operation mode switching control as described above cannot be performed.